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A Contact Sport: The in’s & out’s of wine fermentation

By Debra Meiburg MW

By Debra Meiburg MW

A fermentation tank is like a good dance club: full of energy, heat and bubbles. Surging around the tank is the usual cast of characters: a mob of bacterial hoi-polloi trying to wheedle their way past choosy door bouncers and yeasts strutting into the club with only one thing on their minds – sugar.

When the juice runs out of sugar, the dancing begins to fade, conversation drifts and the exhausted yeasts pass out. By the time the DJ has packed up his kit, the dormant yeasts along with other small bits of party debris are sinking to the bottom of the tank. These passed-out clubbers are called and are classed into two categories. The gross lees, which USA winemakers refer to as mud, are “B list” invitees and the fine lees, which are comprised primarily of dormant yeast cells, are on the “A list.”

After fermentation, winemakers immediately drain the clear juice from the tank and discard the gross lees lounging on the bottom of the tank. Though the juice seems relatively clear, it is laden with lightweight and sleepy yeast cells stirred up by the movement, who begin slow dancing around the liquid in a spiral drift to the bottom of the tank.

These small yeast cells play many roles in the development of a wine’s character. They infuse the wine with attractive yeasty, toasty or biscuit-like flavors and they have an effect on the wine’s texture, or the way wine feels in one’s mouth, by making it seem creamier or thicker. Lees are an attractive cocktail for other organisms that help soften the wine and lees act as an anti-oxidant, protecting wine from the harmful effects of too much oxygen exposure. They also provide a protective barrier between the wine and the interior walls of the oak barrels, which might otherwise impart harsh tannins and overt flavors into the wine.

Lees contact is so beneficial, that winemakers often stir up the lees hovering at the bottom of the tank to promote the uptake of the lees character. If wine is maturing in small oak barrels, which have only a narrow opening at the top, the cellar team stimulates the lees with an instrument that looks more suitable for medieval torture: a slim metal pole with a length of chain on the end. This spin technique is called lees stirring, or bâtonnage in French.

With aromatic grapes, such as Riesling or Chenin Blanc, the yeasty aromas derived from lees contact diminish the wine’s fruity character, so are undesirable. With neutral grapes, such as Chardonnay, lees influence is highly desirable as it adds vibe and dimension to the wine. For some wines, this yeastiness is so integral to the wine’s beat that its label will state “sur lie” or “aged sur lie”, such as the crisp, zingy wine from the Loire Valley, called Muscadet sur Lie. The hottest lees act is in Champagne where winemakers ensure wine has intimate contact with yeast cells by trapping them in the bottle itself, leaving the sludgy yeast layer in the bottle for years, ejecting it only immediately before dressing the bottle for release to market. Or clubs.

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